PLANKTON OF THE GULF OF MAINE 47 



and may almost completely monopolize the water there during the summer. In June 

 and July, too, the eggs or larvae, or both, of sundry summer-breeding fishes, such as 

 silver hake, rosefish, cunner, and witch flounder, appear in the appropriate parts 

 of the gulf to take the place of such spring spawners as the haddock and plaice. 



As summer passes into autumn Sagitta serratodentata continues to spread west- 

 ward right into Massachusetts Bay (p. 322). The hyperiid-amphipod genus Euthemisto 

 likewise works inshore in September and October, so that it is more numerous in 

 the bay then than at any other time of year, and Pleurobrachia may swarm locally, 

 notably off the coast of eastern Maine and at the mouth of the Bay of Fundy. It 

 is during late summer or early autumn, too, that Phialidium is most plentiful and 

 that Salpa? and other tropical forms (p. 53) are most often encountered in the gulf. 



Hand in hand with the autumnal cooling of the surface, the small Phialidium 

 languidum disappears first and then the larger scyphomedusae, either dying at the 

 close of their natural period of life or being destroyed by the fury of the autumn 

 storms. The large, blue copepod Anomalocera likewise vanishes from the waters 

 of the gulf (p. 1S4). On the other hand, ctenophores may be locally abundant until 

 well into the autumn, witness the swarms of Pleurobrachia that appeared off Cape 

 Cod during October, 1916 (p. 367) ; and the small brown copepod Temora longi- 

 cornis becomes so plentiful locally near the land at this season that it dominated 

 the surface catch off Cape Ann on October 31, 1916 (station 10399), when a sample 

 of the copepods consisted of over 100 Temora with but 2 Centropages and 1 Calanus. 

 Doctor McMurrich, likewise, found Temora most regularly and in greatest abun- 

 dance in October, November, and the first half of December at St. Andrews (p. 289), 

 but in the open Gulf no definite seasonal periodicity has been established for it (p. 2S9) . 



Centropages was the most numerous copepod on the surface off Cape Cod in 

 November, 1916 (station 10404), but all our deeper hauls in autumn have been 

 dominated by Calanus, Pseudocalanus, and Metridia, with Euthemisto of both 

 species, Sagitta elegans, Meganyctiphanes, Thysanoessa, and Limacina. In fact, 

 they have paralleled the community characteristic of summer. So few of the bot- 

 tom dwellers of the Gulf breed in October or November that their larvae are practi- 

 cally nonexistant in the plankton at that season; but the presence of juvenile Calanus 

 in the western basin on November 1 (station 10400), of young Aglantha and young 

 Sagitta elegans, of eggs probably referable to the latter, and of an abundance of small 

 as well as large Limacina off Massachusetts Bay at that time (stations 10399 and 

 10403) proves that all these pelagic animals reproduce in the Gulf during October, 

 though probably not in any great abundance. 



I have already pointed out that no general alteration takes place in the zoo- 

 plankton of the Massachusetts Bay region during late autumn and early winter, for 

 our tows gave us much the same yield off Cape Ann at the end of November and in 

 December, 1912, and in January, 1913, 25 as is to be expected there in August, Sep- 

 tember, or October — that is, Calanus dominant, with such other copepods as Pseudo- 

 calanus, Metridia lucens, Centropages, and Euchaeta; the chsetognaths, Sagitta elegans 

 and occasional S. serratodentata; Euthemisto compressa and E. bispinosa; the common 



" These hauls are described in an earlier report (Bigelow, 1914a, p. 404) 

 7589S— 20 4 



